Acid zinc electroplating

ABSTRACT

ACID ZINC ELECTROPLATING BATHS AT PH 2.5 TO 5.5 ARE PROVIDED WHICH USE AS ADDITIVES COMPOUNS WITH THE GENERAL FORMULA:   1-(YX-),3-R,R&#39;&#39;-PYRIDINIUM Z(-)   WHEREIN R IS -CONH2, -CH, -CONHNH2, -COOH OR -COOR &#34;COOR&#34; WHERE R&#34; IS AN ALKYL GROUP OF 1 TO 4 CARBON ATOMS, R&#39;&#39; IS HYDROGEN, HALOGEN OR AN ALKYL GROUP OF 1 TO 4 CARBON ATOMS, X IS AN ALKYL GROUP OF 1 TO 8 CARBON ATOMS, Y IS -COOH, -COO-, -SO3H, -SO3- OR -CONH2, AND Z- IS A HALIDE ION OR IS ABSENT WHEN Y IS -COO- OR -SO3-.

ACID ZINC ELECTROPLATING John Derek Rushmere,- Wilmington, Del., assignor to 1 du Pont de Nemours and Company, Wilmington,

No'DrawingiFiled June 28,1971, Ser. No. 157,662 ""IntJ'Cl. C23b /12, 5/46 ."Cli'ZOkSS R"- 12 Claims on THE niscLoSURn r Acid-zinc electroplatingbaths at pH 2.5 to 5.5 are provided which use as additives compounds with the general formular' w than v r s Hz. -'-CN,, -'CONHNH --COOH or -COOR"where R" is an alkyl group oil to 4 carbon Ri'is' hydrogen, halogen or an alkyl group of 1 to4 carbon atoms,

X is an alkyl group of 1 to 8 carbon atoms,

Y is -COOH, -COO", -SO;1;H, S0 or --CONH and- Z"- is 'a halide ion or is absent when Y is C0O" or Heretofore, bright decorative zinc plates have been customarily obtained from alkaline cyanide zinc baths or alkaline zincate baths, whereas acid zinc baths have been used where the appearance of the deposited zinc is not especially important as in the coating of steel strip or conduit. With increasing industry emphasis on pollution control and the diminution of cyanide plating baths, the art in acid zinc plating is being increasingly directed to additives useful for improving the appearance of the zinc deposit over awide current density range.

; Numerous patents concerned with bright zinc deposits obtained from acid zinc baths have issued over the years. Many of these have been directed to the use of sulfur and nitrogen compounds such as thioureas, pyridine (U.S. Pat. 2,355,505 issued to John L. Bray and Robert E. Howard on Aug. 8, 1944), sulfonated heterocyclics (US. Pat. 2,543,545 issued to Charles L. Faust and Arthur E. Bearse on Feb. 27, 1951), alkylamines or polyamines as additives to improve brightness; a recent patent US. 3,537,959 issued to Joachim Korpiun and Hans J. Steeg is directed to the use of primary amines and naphthalene sulfonic acid-formaldehyde condensation products for this purpose.

Quaternary nitrogen compound additives useful in alkaline zinc electroplating are described in US. Pat. 3,318,787 issued to Gustav Rindt, and Donald H. Becking on' May 9, 1967, and US. Pat. 3,411,996 issued to John D Rushmere on Nov. 19, 1968.

SI JYI VIMARYZOF THE INVENTION According to the present invention there is provided an aqueous acid zinc electroplating bath comprising an 3mm Pa s 0 "Ice aqueous solution of a zinc salt maintained at a pH in the range of about 2.5 to 5.5 and having dissolved therein in an amount effective to give a bright zinc deposit a pyridinium compound of the general formula:

wherein R is -CONH -CN, CON'HNH -CO0H or -COO where R is an alkyl group of 1 to 4 carbon atoms,

R is hydrogen, halogen or an alkyl group of 1 to 4 carbon atoms,

X is an alkyl group of 1 to 8 carbon atoms,

Y is COOH, -COO-, -SO H, S0 or CONH and Z is a halide ion or is absent when Y is --COO- or Also provided is a process of electroplating bright zinc using the above acid zinc electroplating bath.

DETAILED DESCRIPTION OF THE INVENTION Generally, the invention pertains to the electro-deposition of zinc from acid zinc plating baths known to those skilled in the art. These baths can be formed by the dissolution of zinc oxide in an excess of a common noncomplexing acid such as sulfuric, sulfamic, fluoboric or hydrochloric with the pH of the bath adjusted to be tween about 2.5 and 5.5, preferably between 3.5 and 4.5, by the addition of aqueous ammonia. Alternatively, the baths can be formed by the dissolution of commercial zinc and ammonium salts, such as the sulfates, acetates, chlorides, fluoborates or sulfamates, in water with subsequent adjustment of pH to the normal range by means of aqueuos ammonia, an alkali metal base or acid as required. Mixtures of zinc salts can be used if desired. Temperature of operation is usually at ambient temperatures, but can be between 15 C. and 45 C. Other metal salts such as sodium sulfamate or potassium sulfate may be added to enhance electrical conductivity.

Zinc electrodeposits obtained from such acid baths are typically coarse and dull gray in appearance and have little commercial value, especially in the decorative plating of screws, chains and other items of hardware. It has now been found that when certain quaternized pyridine compounds are added singly or in combination to an acid zinc electroplating bath of the type described above in amounts from 0.2 to 20 grams per liter, preferably 2 to 8 grams per liter, the resultant zinc electroplate is smooth and bright, and of commercially acceptable quality. Excellent throwing power is also usually obtained from baths using these compounds as is demonstrated by uniform plating between the threads and in the head recesses of ordinary Wood screws. The quaternized pyridine compounds useful in the present invention have the general formula:

wherein R is CONH -CN, CONHNH -COOH or COOR where R" is an alkyl group of 1 to 4 carbon atoms,

R" is hydrogen, halogen or an alkyl group of 1 to 4 carbon atoms,

3 X is an alkyl group of 1 to 8 carbon atoms, Y is --COOH, -CO", SO H, SO or CONH and Z- is a halide ion or is absent when Y is COO- or Preferred compounds are where R is --CONH or CN, R' is hydrogen, X is alkyl of 1 to 4 carbon atoms, Y is SO H, SO or -CONH and Z- is chloride ion or is absent when Y is 80 Particularly preferred compounds are l-(3-propanesulfonate) 3-cyano pyridinium betaine and I-(Z-acetamido) 3-amido pyridinium chloride. Other compounds which have been found useful in the plating of zinc from acid baths are:

. 1-(3-propane sulfonate) 3-amido pyridinium betaine l-(2-diethylacetic acid) Z-amido pyridinium bromide 1-(2-isobutyric acid) 3-amido pyridinium chloride 1-(3-propane sulfonate) 3-carbomethoxy pyridinium be taine 1-(2-proprionic acid) 3-amido pyridinium chloride l-(2-octanoic acid) 3-amido pyridinium bromide 1-(2-acetamido) 3-hydrazido pyridinium chloride 1-(2-acetic acid) 3-carboxy pyridinium chloride Further compounds within the general formula useful in the invention are:

9. 1-(2-acetamido) 3-amido 4-bromo pyridinium chloride 10. l-(3-pyropanesulfonate) 3-cyano S-methyl pyridinium betaine 11. 1-(2-isobutyric acid) 3-amido 6-chloro pyridinium chloride 12. 1-(2-propionic acid) 3-amido 6-ethyl pyridinium chloride.

The compounds within the scope of the invention are not all equally effective under all conditions. Thus, some are preferred for still or automatic rack plating, whereas others are more effective for barrel plating or other plating operations. However, the compounds described have been found capable of improving the quality of zinc plate deposited from acid zinc baths.

It should be understood that the quaternized pyridine compounds described have been used both in the form of betaines which undergo no further ionization in solution and in the form of normal salts which undergo ionization on dissolution in the plating bath. Thus, where appropriate, the betaine and normal salt forms are essentially the same compounds. For instance, 1-(3-propanesulfonate) 3-cyano pyridinium betaine is equivalent in the bath to 1-(3-propanesulfonic acid) 3-cyano pyridinium chloride.

In the examples which follows, the following plating bath was used unless otherwise indicated.

ZnSO --140 .g./1. H4)2 4 g/ pH3.5 Temp-25 C.

The invention can be further understood by referring to the following examples in which parts and percentages are by weight unless otherwise indicated:

EXAMPLE 1 To a Hull Cell containing 267ml. of the acid zinc sulfate plating bath was added 1 g. of 1-(2-acetamido), 3- amido pyridinium chloride prepared by precipitation from a refluxing ethanolic solution of nicotinamide and Z-chloroacetamide. A steel panel was then plated at 2 amps. for minutes to obtain a deposit of smooth bright zinc over the CD. range 1-65 amp/ft.

EXAMPLE 2 One g. of l-(3-propane sulfonate), 3-cyano pyridinium betaine prepared by precipitation from a refluxing acetone solution of 3-cyano pyridine and propane sultone was added to 250 ml. of acid zinc sulfate plating bath and barrel plated at 1.5 amps. 'for 3 0'minutes A shiny bright product was obtained 'which required no bright 'dip.

A second 30 g. batch of'screws werezplated:from .this solution at low. current density, namely 0.5 amp.- for-' 30 minutes. Again a shiny bright product was obtained which required no bright dip.

EXAMPLE, 4

To 1.2 1. of acid zinc sulfate bath was added 2 g. of 1-(2-diethylacetic acid) 3-amido pyridinium bromide plus 2 g. of I-(Z-acetamido) 3-amido pyridinium chloride. A steel Hull Cell panel, bent in the form of a rectangular Z was then zinc plated at 2 amps. for 10 minutes. Each minute the work was removed from the bath for 2-5 seconds to simulate conveyance on an automatic rack plater, and also help detach gas bubbles which might otherwise cause pitting. At the end of the plating period, the shape was bright and shiny with even coverage into' the recesses.

EXAMPLE 6 An acid zinc-plating bath was prepared containing:

To ml. of this bath was added 0.4 g. of '1-(3-propane sulfonate) 3-cyano pyridinium betaine and the bath then used to zinc plate 30. g. of #6 x /2 wood screwsat 1.5 amps. for 20 minutes in a mini-barrel. After plating'and a brief dip in 0.1 percent nitric acid, the screwswere smooth, semi-bright and of acceptable commercial quality.

EXAMPLE 7 The bath of Example 6 was diluted withwater to'give 250 m. of a bath now containing:

With no further addition of additives this bath gavezinc deposits that were dull and of unacceptable quality. However after the addition of a further 0.4 g. of 1-(3-propane sulfonate) 3-cyanopyridinium betaine and-0.5 g. of .1-(2- diethylacetic acid) 3-amido pyridinium bromide, 30 .g. of #6 x /2 w0od screws plated at 1.5 amps. for 10 minutes gave a shiny bright'product. The screws took an excellent chromate conversion coating;

wherein R is CONH CN, CONHNHg, COOH or OOOR" Where R" is an alkyl group of l to 4 carbon atoms,

R is hydrogen, halogen or an alkyl group of 1 to 4 carbon atoms,

X is an alkyl group of 1 to 8 carbon atoms,

Y is COOH, COO-, SO H, SO or CONH and Z- is a halide ion or is absent when Y is COO- or 2. The acid electroplating bath of Claim 1 wherein the pyridinium compound is added to give a bath concentration within the range of about 0.2 to 20 grams per liter.

3. The acid electroplating bath of Claim 2 wherein the pyridinium compound is selected from the group consisting of 1-(3-propanesulfonate) 3 cyano pyridinium betaine and I-(Z-acetamido) 3-amido pyridinium chloride.

4. The acid electroplating bath of Claim 2 wherein the pH of the bath is within the range of about 3.5 to 4.5.

5. The acid electroplating bath of Claim 4 wherein the pyridinium compound is added to give a bath concentration within the range of about 2 to 8 grams per liter.

6. The acid electroplating bath of Claim wherein the pyridinium compound is selected from the group consisting of l-(3-propanesulfonate) 3-cyano pyridinium betaine and I-(Z-acetamido) 3-amido pyridinium chloride.

7. In a process of electroplating bright zinc from an aqueous acid zinc electroplating bath having a zinc salt dissolved therein the improvement comprising maintaining said bath at a pH in the range of about 2.5 to 5.5 and adding thereto in an amount efiective to give a bright zinc deposit a pyridinium compound of the general formula:

wherein R is CONH CN, CONHNH --COOH or COOR" where R" is an alkyl group of 1 to 4 carbon atoms,

R is hydrogen, halogen or an alkyl group of l to 4 carbon atoms,

X is an alkyl group of 1 to 8 carbon atoms,

Y is COOH, COO, SO H, SO or CONH and Z" is a halide ion or is absent when Y is COO or 8. The process of Claim 7 wherein pyridinium compound is added to give a bath concentration within the range of about 0.2 to 20 grams per liter.

9. The process of Claim 8 wherein the pyridinium compound is selected from the group consisting of 1-(3- propanesulfonate) 3-cyano pyridinium betaine and 1-(2- acetamido) 3-amido pyridinium chloride.

10. The process of Claim 8 wherein the pH of the bath is within the range of about 3.5 to 4.5 and the pyridinium compound is added to give a bath concentration within the range of about 2 to 8 grams per liter.

11. The process of Claim 10 wherein the pyridinium compound is selected from the group consisting of 1-(3- propanesulfonate) 3-cyano pyridinium betaine and 1-(2- acetamido) 3-amido pyridinium chloride.

References Cited UNITED STATES PATENTS 2,543,545 2/1951 Faust et al. 204 R 2,813,065 11/1957 Du Rose 20445 3,203,878 8/ 1965 Willmund et al 204-52 3,318,787 5/1967 Rindt et al 204-55 Y 3,594,291 7/1971 Todt et al. 204-55 R FOREIGN PATENTS 805,316 12/ 1958 Great Britain.

1,202,525 8/ 1970 Great Britain.

FREDERICK C. EDMUNDSON, Primary Examiner US. or. X.R. 204-Dig. 2 

